A finally shaped paper-made container filled with liquid foods such as a juice and a milk is obtained by forming a web-like packaging laminated material having a predetermined folding line in tubular shape, longitudinally sealing in the longitudinal direction of the tube, filling foods into the tubular packaging material, pressing the tubular packaging material in the predetermined intervals to seal the same by transversal seal in transversal direction, cutting at the center of the transversal seal zone to obtain a pillow-like preliminary forming, and sealing the flap containing the transversal seal zone formed by folding along the folding line on the side wall of the container and bottom face of the container.
FIG. 1 shows an outline of one example of a filling packaging machine for the paper-made container. The filling machine shown in this example winds out a packaging material web 1 having thermoplastic material layer on the inner and outer layers, wound in roll shape, and transfers it in the filling machine by rollers. A strip tape 2 is bonded to one end of the packaging material web by a strip tape applicator 3. The packaging material web is sterilized by passing through a sterilizing bath 4. Sterilizing agents are removed by an air knife 5. The tubular packaging material is formed by a forming roller 6. An overlap is formed by lapping both ends of the packaging material. The overlap is longitudinally sealed in the tube longitudinal direction by a longitudinal seal element 8. Liquid food is filled into the tube from a filling pipe 7. This tube, while being sent downward by a length equivalent to one packaging container, is sandwiched by a sealing jaw 10 and an oppositely arranged jaw 11. Two transversal seal zones are formed by the transversal seal in the crossing direction. A pillow-like preliminary forming 12 is continuously formed. The middle of the seal zone of the connected pillow-like preliminary forming is cut by knife or the like, and the forming is separated to individual pillow-like preliminary forming 13. A finally shaped packaging filling container 14 by folding flaps on the upper and lower of the separated pillow-like preliminary forming at a final folder 15.
FIG. 2 shows a feature in which the pillow-like preliminary forming 13 is folded at the final folder 15. The pillow-like preliminary forming 13 is sealed by two transversal (transversal line) seal zone 23 and longitudinal seal zone 26. The pillow-like preliminary forming 13 has side walls 22, 22b and 22a defined by the folding lines (refer to FIG. 2(a)).
As shown in FIG. 2(b), the main body of the pillow-like preliminary forming is formed in rectangular solid along folding lines. On the edge, the transversal seal zone 23 and flaps 24, 25 are formed to be upright from the container wall. The transversal seal zone 23 is upright from the bottom face 22b and the top face 22a. The flaps 24 and 25 integrally communicate with the container wall through ridge sides 25a and 24a. 
Next, as shown in FIG. 2(c), after the transversal seal zone 23 is folded, the flaps are rotated around the ridge side as a center. A container top side flap 24 folded into the side wall 22, and the container bottom side flap 25 is folded into the bottom face 22b. 
FIG. 3 shows a perspective view of outline of rectangular solid liquid food filling paper-made container. The container 14 has the transversal seal zone 23 and longitudinal 26 running to the bottom face from the container walls 22 and 22a and the top wall 22a through the container wall on the back. The folded flap 24 is provided through the ridge side 24a. 
Sufficient sealing must be carried out at the above-mentioned seal zone so as to prevent the liquid food contained in the container from leaking and being exposed to external air. However, if the temperature and pressure on the transversal seal are improper, the melted thermoplastic material on the packaging laminated material may protrude into the container in which the content is filled. The melted substance directly contacts the contained liquid foods, and becomes brittle by sharply cooling, and the laminated material may be broken from the protruded location. For sealing, it is necessary to obtain a transversal seal whose melted substance does not protrude into the container.
Then, liquid food containers made by the filling packaging machine are regularly sampled by the operator of the machine for inspection. For the sampled container, the flap is peeled from the container wall so as to change the rectangular solid container to pillow-shaped by a substantially reverse method of the container final shape forming, that is, a method reverse to the method in which the flap is folded by the final folder of the filling packaging machine.
The transversal seal is inspected by visually measuring the seal strength, and presence or absence of pinhole, in addition, an edge on the inside of the container on the transversal seal zone for unevenness on the outer surface over the whole length of the outer surface of the edge.
In the conventional edge appearance inspection of the transversal seal, for the containers regularly sampled by the operator, the appearance on the inside of the edge of the transversal seal is visually observed, and then presence or absence of thermoplastic resin such as polyethylene protruded from the transversal seal zone is checked. Because the projection is transparent, it is not easy to find it and it is difficult to securely capture fine uneven defects.
There occur some variations in inspection due to individual difference in operator in the inspection for inspecting a melted thermoplastic material of the transversal line seal protrusion into inside, thereby reliability of the inspection is getting lower, and then more accurate and reliable inspection is required.